Szabolcs wrote:
> Josef Otta wrote:
>> Hi all,
>>
>> I have a question to a catching error messages is the evaluation of
>> graphics functions in the version 6. For example, consider a function
>> plotting with non real values:
>>
>> {Plot[Sqrt[x], {x, -2, 1}],
>> $MessageList}
>>
>> in version 5.2 the output is a plot with these messages
>>
>> {Plot::plnr, Plot::plnr, Plot::plnr, General::stop}}
>>
>> If I use the same approach in the version 6.0 i get no error messages
>> and that is a big problem for me. Do you have any idea how to get
>> these errors?
>> I do not know how to get these messages also in the cases where
>>
>> Complex, ComplexInfinity, Indeterminate, Null, Underflow or Overflow
>>
>> occur in the evaluation of almost every graphics function.
>
> I would like to know this too. On[General::plnr] turns on this warning
> message. However, the message is only issued when Plot encounters a
> symbolic expression. It does not work for complex numbers, infinity etc.
>
> And I do not understand why this new General::plnr is turned off by
> default. Passing a completely non-numerical argument (as opposed to a
> function that evaluates to complexes in some regions) to Plot is an
> unintentional mistake in 99% of the cases. The only time I turned off
> Plot::plnr in 5.2 was when repeatedly plotting things like Plot[Sqrt[x],
> {x, -1, 1}], but these kinds of examples do not warn with Plot::plnr any
> more in Mathematica 6 (even though it would often be useful).
I for one am glad that I no longer see those annoying "not a machine
size real number" messages. It's no longer a problem to plot a function
across an interval where it is not real. For example, I can now plot
ArcSec[x] for {x,-5,5} and get a nice looking plot, or plot Sqrt[x]
together with Sqrt[x+5] on {x,-5,5} without having to plot them
separately and Show. To me this is an improvement.
On a somewhat related topic, I really like the new Exclusions option.
--
Helen Read
University of Vermont